The present invention relates to generation of hydrogen by electrolysis of aqueous organic solutions, and more specifically to an electrolysis system with a solid electrolyte membrane cell for producing hydrogen.
Hydrogen is known to have many applications ranging from synthesis of chemicals such as ammonia, petroleum refining in producing high octane gasoline and aviation jet fuel and in removal of sulfur, hydrogenation in various industrial processes, to propellant fuels in combination with oxygen or fluorine for rockets and spacecraft. Pure hydrogen usually takes a form of a colorless, odorless, and tasteless gas composed of diatomic molecules, H2, under ordinary conditions. Alternatively, pure hydrogen may also be stored in the liquid phase under a certain pressure. Pure hydrogen is usually produced by producing the hydrogen gas.
One conventional method of producing the hydrogen gas is by electrolysis of water. This is a simple process in which water (H2O) is decomposed into hydrogen (H2) and oxygen (O2) by electrochemical reactions at the electrodes in an electrolytic cell. The cost of hydrogen generation by electrolysis of water is mainly determined by the cost of energy consumption since the cost of equipment diminishes over many production cycles. The energy consumption in an electrolysis process can be indicated by the operating voltage applied to the electrodes in the electrolytic cell. In ordinary operating conditions, the higher the operating voltage, the larger the energy consumption. A typical operating voltage for electrolysis of water is approximately about 1.4 Volt or higher.
Due to the simplicity of electrolysis process and the equipment, conventional water-based electrolysis systems are widely used in portable or stationary hydrogen generators for small and large scale hydrogen generation. Specifically, hydrogen generation devices can be used as fuel supply for fuel cells that generate electricity by consuming hydrogen.
The inventors recognized that it could be useful to produce hydrogen based on devices using an alternative fuel. The present disclosure describes an alternative electrolysis system for producing hydrogen. According to a first aspect of the invention, an aqueous organic solution, rather than water, is used in an electrolytic cell for producing the hydrogen gas. A preferred organic solution is the type having an operating voltage lower than that of the water in an electrolysis process. Use of this type of organic solutions reduces the energy consumption and therefore the cost of the generated hydrogen gas.
According to one embodiment of the invention, a preferred organic solution is methanol, CH3OH. The electrolysis of methanol to hydrogen and carbon dioxide can occur at a low operating voltage of about 0.4 V. This may lead to a significant reduction in energy consumption of more than 70% compared to electrolysis of water. The cost of hydrogen produced by using the present invention, including the cost of the methanol, may be about 50% of the usual amount of hydrogen produced by the electrolysis of water.
Another aspect of the invention is the construction of the electrolytic cell. A preferred cell has an integrated membrane-electrode assembly which includes two catalyzed electrodes each bonded to one side of a solid proton-conducting polymer membrane. The solid polymer serves as the electrolyte. One advantage of the solid membrane electrolytic cell is elimination of the conventional liquid acidic or alkaline electrolyte which can cause various problems including corrosion of cell components, poor activity of catalysts, and parasitic shunt currents. The solid membrane electrolytic cell can also be made robust and compact.
Yet another aspect of the invention is a power generation system having a hydrogen fuel cell and a hydrogen generator based on electrolysis of an organic fuel.